Nonvolatile memory is often used in various devices, such as computers. Nonvolatile memory is a type of memory storage that can retain data even while it is not powered on. Examples of nonvolatile memory include flash memory, electrically programmable read-only memory (EPROM), and electrically erasable programmable read-only memory (EEPROM). Functionality of nonvolatile memory includes programming, read, and erase operations.
Each of the nonvolatile memory units can be formed as a field-effect transistor, including a floating gate and a control gate. The floating gate can be configured to hold charge and is fabricated on an oxide layer over an active region of a semiconductor substrate. The floating gate can be separated from source/drain regions in the semiconductor substrate by the oxide layer.